Does environmental exposure to the greenhouse gas, N 2 O, contribute to etiological factors in neurodevelopmental disorders? A mini-review of the evidence.

BACKGROUND: Neurodevelopmental disorders are increasing in prevalence worldwide. Previous work suggests that exposure to the environmental air pollutant and greenhouse gas - nitrous oxide (N2 O) - may be an etiological factor in neurodevelopmental disorders through the targeting of several neural correlates.

METHODOLOGY: While a number of recent systematic reviews have addressed the role of general anesthesia in the surgical setting and neurodevelopmental outcomes, a narrative mini-review was conducted to first define and characterize the relevant variables (i.e., N2 O, attention-deficit hyperactivity disorder [ADHD] and autism spectrum disorders [ASD]) and their potential interactions into a coherent, hypothesis-generating work. The narrative mini-review merges basic principles in environmental science, anesthesiology, and psychiatry to more fully develop the novel hypotheses that neurodevelopmental impairment found in conditions like ADHD and ASD may be due to exposure to the increasing air pollutant, N2 O.

RESULTS: The results of the present mini-review indicate that exposure to N2 O, even at non-toxic doses, may modulate central neurotransmission and target many neural substrates directly implicated in neurodevelopmental disorders, including the glutamatergic, opioidergic, cholinergic, and dopaminergic systems. Epidemiological studies also indicate that early and repeated exposure to general anesthesia, including N2 O, may contribute to later adverse neurodevelopmental outcomes in children.

CONCLUSIONS: The current evidence and subsequent hypotheses suggest that a renewed interest be taken in the toxicological assessment of environmental N2 O exposure using validated biomarkers and psychiatric endpoints. Given the relevance of N2 O as a greenhouse gas, societies may also wish to engage in a more robust monitoring and reporting of N2 O levels in the environment for climactic benefit as well.